Ice can take on a variety of forms in caves similar to the most common
of depostional formations, such as stalactites, stalagmites, flowstone,
and curtains. These typically form from water flowing or dripping into
the cave, and crystal faces aren't evident. More unusual forms such
as harilike strands and hexagonal crystals may occur when ice freezes
from water vapor.

In almost any cave in areas that reach below freezing temperatures
in winter, ice formations may be seen in entrance zones regardless of
the ambient temperature further in the cave. Lava tubes often act as
cold air traps, with cold winter air sinking and allowing ice formations
to form that may persist well after surface temperatures have risen
in the spring. As warmer air wafts through the cave, it may melt the
ice into bizarre rounded shapes with bulbous tops known as schmos.

The most spectacular ice formations are those in alpine caves where
the cave's ambient temperature stays at or below the freezing point
year-round. One of the best known of these is the touristic Eisriesenwelt
Cave in Austria. In the USA, few of these are known but perhaps the
best-known is the undeveloped Fossil Mountain Ice Cave of Wyoming.

The terminology for caves with perennial ice has been a bit confused. They have long been called sinply "ice caves" in English. Englishman Edwin Swift Bach suggested that these
caves be named by their French name, Glacieres, in his seminal 1900 work Glacieres and Freezing Caverns. But even Edwin acknowledged that people were unlikely to adopt the French term, and "ice cave" continues to be the most popular term used for these caves by both the public and most geologists. Caves actually formed IN ice are commonly called Glacier
Caves by glaciologists.

Broomstick ice stals in a lava tube

Massive ice deposits in a lava tube

Permanent ice can take on a blue-green cast.

Deflected ice stalactites and stalagmites in a lava tube

Where water flows along freezing ceilings, ice draperies can form.

Hexagonal ice crystals on the ceiling in a limestone cave. These form from water
vapor.